Abstract

Rhesus monkeys are widely used as animal models of human attention. Such research rests upon the assumption that similar mechanisms
underlie attention in both species. Here, we directly compare the influence of low-level stimulus features on overt attention in
monkeys and humans under natural conditions. We recorded eye-movements in humans and rhesus monkeys during free-viewing of natural
images. We find that intrinsic low-level features, such luminance-contrast, texture-contrast and saliency—as predicted by a standard
model, are elevated at fixation points in the majority of images. These correlative effects are not significantly different between species.
However, local image modifications affect both species differently: moderate modifications, which are in the range of natural fluctuations,
attract overt attention in monkeys significantly stronger than they do in humans. In addition, humans show a higher inter-individual
consistency regarding which locations they fixate than monkeys, in spite of the similarity for intrinsic low-level features. Taken together,
these data demonstrate that—under natural conditions—low-level stimulus features affect attention in monkeys and humans differently.

Received 3 February 2005; received in revised form 11 May 2005.
�c2005 Elsevier Ltd.
We thank Honda RI Europe (W.E.), Volkswagen Foundation, (W.K., and K.P.H., grant ‘‘Plasticity of Spatial
Cognition’’), Deutsche Forschungsgemeinschaft (KPH, SFB 509 ‘‘Neurovision,’’ TP B2) and the Swiss National
Science Foundation (W.E., project-no: PBEZ2–107367; PK, Grant No. 31-61415.01) for their financial support.
We are grateful to D. Walther for supplying a stand-alone matlab-implementation of the saliency-map model and to A. Horstmann and Dr.W. Lindner for their technical assistance in carrying out the experiments.